The present invention disclosed and claimed herein pertains generally to the field of neutron detection devices and, more particularly, to neutron detection devices of the type which employ a metal housing known as a "log" which contains an ionizable counting gas.
In many applications, neutron detectors are weight limited such that reducing the total package weight is important either for the weight reduction for a given sensitivity or for an increase in sensitivity for a given allowed weight. Current neutron detector systems use .sup.3 He or .sup.10 BF.sub.3 gas as the neutron sensing material. This gas is often contained in a metal housing or "log" which weighs about 15 pounds and is approximately 40 mils thick. Such gas filled "logs" are then surrounded with a polyethylene moderator material which is typically a cylindrically shaped sleeve having a wall thickness of approximately 1 to 3 centimeters. This plastic sleeve is slipped over the metal log and serves as a moderator to reduce the energy of the neutron flux to thermal energies where the detecting material has a high neutron capture cross section. The metal case of such prior devices is typically made of stainless steel in order to be mechanically strong enough to withstand pressure changes, handling abuses and the like. In addition, the metal case serves as the ground plane for the counting wire, as an electrostatic shield and as an impermeable barrier between the active materials inside the detector and the external atmosphere. If the active isotope is .sup.3 He which also is the counting gas, the helium must be contained within an electrical conductor since helium will diffuse through insulators.
The hydrogen atoms in the polyethylene material are the important neutron moderator. A solid hydrocarbon form is an efficient method of achieving a high number density of hydrogen atoms near the detector element. In the past the active sensor, "log", and the moderator have been structurally independent. The log with the metal case was self supporting and was slid into the moderator material which was also self supporting.